Method of producing radial tire for construction vehicle

ABSTRACT

A method of producing a radial tire for a construction vehicle, the method enabling a vast reduction in facility costs. A first green tire is formed in a first step molding machine and then removed from it. After that, a vulcanizer bladder unit is installed on the tire. The tire is inflated by the vulcanizer bladder unit and then again placed in the first step molding machine with the vulcanizer bladder unit installed. After that, on the first step molding machine, belts and tread rubber are adhered to the outer periphery of the tire to form a completed green tire. Then the completed green tire, with the vulcanizer bladder unit, is assembled in a vulcanizing mold for vulcanization.

FIELD OF THE INVENTION

The present invention relates to a method of producing a radial tire fora construction vehicle, and more specifically to a method of producing aradial tire for a construction vehicle which enables costs forproduction facilities to be reduced.

BACKGROUND ART

In general, an increasing number of tires of a radial structure havebeen produced to meet needs from users in the field of large-sized tiresfor construction vehicles which are termed as OR tires (Off-the-RoadTires). A method of producing such a radial tire is usually performedwith the following procedure. To begin with, a first green tire whichhas only a tire carcass including a carcass ply and a bead core isformed by use of a first step molding machine. By use of a second stepmolding machine, subsequently, the first green tire is inflated to havean external diameter of a predetermined size, and belts and tread rubberare wound around the outer periphery of the first green tire thusinflated. Thereby, the first green tire is formed into a completed greentire. Thereafter, the completed green tire is cured by use of a curingmachine.

Heretofore, Japanese patent application Kokai publication No.Sho.49-15776 has proposed a measure for improving a method of producinga pneumatic radial tire, according to which a single bladder is useddually as an inflating bladder of the second step molding machine and asan inflating bladder of the curing machine, thereby simplifying theproduction facilities. However, what costs most in the facilities forproducing radial tires is the first step molding machine and the secondstep molding machine. According to the aforementioned measure forimproving the method of producing a pneumatic radical tire, the firststep molding machine and the second step molding machine are still therequired facilities. For this reason, the aforementioned measure stillneeds not only large costs for these machines but also a large spacewhere the machines are installed. As a consequence, the proposed measurehas not been a fundamental measure for improving the method of producinga pneumatic radial tire.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of producing aradial tire for a construction vehicle which causes facilities costs forthe first step molding machine and the second step molding machine to bereduced to a large extent.

In order to achieve the aforementioned object, a method of producing aradial tire for a construction vehicle according to the presentinvention is characterized in that a first green tire is formed by afirst step molding machine; thereafter, the first green tire is removedfrom the first step molding machine; a vulcanizer bladder unit isinstalled on the first green tire thus removed, and the first green tireis inflated by the vulcanizer bladder unit; subsequently the first greentire is once again placed in the first step molding machine while thevaulcanizer bladder unit is still being installed to the first greentire; belts and tread rubber are adhered to the outer periphery of thefirst green tire on the first step molding machine, thus forming thefirst green tire into a completed green tire; and the completed greentire is assembled into a vulcanizing mold while the vulcanizer bladderunit is still being installed to the completed green tire, therebyvulcanizing and forming the completed green tire.

In general, the conventional first step molding machine for forming thefirst green tire does not include a bladder, since no inflatingoperation is performed during the molding step. On the other hand, thesecond step molding machine needs to perform the operation of inflatingthe first green tire. For this reason, as long as the first step moldingmachine is constituted as to be a conventional structure, the first stepmolding machine cannot be dually used as the second step moldingmachine.

However, according to the present invention, a vulcanizer bladder unitindependent from the molding machine is installed to the first greentire which has been formed by the first step molding machine, and thefirst green tire is inflated by this vulcanizer bladder unit.Thereafter, this first green tire is once again placed in the first stepmolding machine while the vulcanizer bladder unit is still beinginstalled to the first green tire. Then, belts and tread rubber areadhered to the first green tire. In this manner, the second step moldingprocess is performed. This procedure no longer requires the specializedsecond step molding machine. As a consequence, the present invention notonly entails no facilities costs for the specialized second step moldingmachine, but also requires no space in which the second step moldingmachine would otherwise be installed. Accordingly, the present inventionenables costs to be reduced to a large extent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram showing a process of forming a firstgreen tire by use of a first step molding machine according to thepresent invention.

FIG. 2 is an explanatory diagram showing a process of forming the firstgreen tire following the process of FIG. 1 by the first step moldingmachine.

FIG. 3 is an explanatory diagram showing a process of forming the firstgreen tire following the process of FIG. 2 by the first step moldingmachine.

FIG. 4 is an explanatory diagram showing a process of installing avulcanizer bladder unit to the first green tire which has been removedfrom the first step molding machine.

FIG. 5 is a cross-sectional view showing a condition in which thevulcanizer bladder unit has been installed to the first green tire.

FIG. 6 is a cross-sectional view showing a condition in which the firstgreen tire in the condition of FIG. 5 is inflated by use of thevulcanizer bladder unit.

FIG. 7 is an explanatory diagram showing a process of placing the firstgreen tire in an inflated condition, which is obtained in FIG. 6, in thefirst step molding machine once again.

FIG. 8 is an explanatory diagram showing a process of winding beltsaround the first green tire which has been placed in the first stepmolding machine.

FIG. 9 is an explanatory diagram showing a process of obtaining acompleted green tire by winding tread rubber around the outer peripheryof the belts following the step of FIG. 8.

FIG. 10 is an explanatory diagram showing a process of vulcanizing thecompleted green tire, which has been obtained in the process of FIG. 9,in a vulcanizing mold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 3 are diagrams respectively showing examples of a process offorming a first green tire by use of a first step molding machineaccording to a step sequence in a method of producing a radial tire fora construction vehicle according to the present invention.

Reference numeral 100 denotes a first step molding machine. In the firststep molding machine 100, reference numerals 1 and 2 respectively denotea headstock and a tailstock. The headstock 1 is provided with a driveshaft 3. A forming drum 5 is mounted detachably onto the drive shaft 3.The forming drum 5 is configured changeably to extend and reduce itsradius. In addition, the tailstock 2 is provided with a driven shaft 4.The driven shaft 4 is designed to rotate in conjunction with the driveshaft 3 and the forming drum 5. A bead supplying unit 6 a is fitted tothe drive shaft 3, and a bead supplying unit 6 b is fitted to the drivenshaft 4. The bead supplying units 6 a and 6 b are designed toreciprocate on the drive shaft 3 and the driven shaft 4 respectively.Thereby, the bead supplying units 6 a and 6 b come close to, and apartfrom, the forming drum 5.

With regard to the process of forming a first green tire, first of all,as shown in FIG. 1, a cylinder-shaped band 7 which has been separatelyformed in advance by a band forming machine, which is not illustrated,is mounted onto the forming drum 5 of the first step molding machine100. In addition, a bead core assembly 8, which has been formed byfitting a bead filler 8 f of green rubber to a ring-shaped bead core 8c, is attached to each of the bead supplying units 6 a and 6 b. The beadcore 8 c is formed by winding steel wire in a ring several times. Thecylinder-shaped band 7 is formed by using a carcass ply 9 as a base. Inthe carcass ply 9, organic fiber cords or steel cords are arranged inparallel in the drum-axis direction. An inner liner layer made of rubberwith no permeability to air is applied to the inner periphery of thecarcass ply 9. In addition, reinforcement plies 10 and 10 are adheredrespectively to the two end portions of the outer periphery of theforming drum 5 in the axis direction.

Subsequently, the end portions 9 e and 9 e of the carcass ply 9 arefolded inward in the radial directions respectively as shown with brokenlines. Then, the bead supplying units 6 a and 6 b. are displacedrespectively toward the two end portions of the forming drum 5 to thefolded end portions 9 e and 9 e, and the bead core assemblies 8 and 8respectively on the bead supplying units 6 a and 6 b are transferredrespectively to the end portions 9 e and 9 e of the carcass ply 9.

Thence, the end portions 9 e and 9 e of the carcass ply 9 are foldedback in a way that the bead core assemblies 8 and 8 are wrappedrespectively in the end portions 9 e and 9 e of the carcass ply 9.Thereby, the end portions 9 e and 9 e are put into a condition as shownin FIG. 2. Furthermore, as shown in FIG. 3, two sheets of side rubber 11and 11 are wound around the outer peripheries of the end portions 9 eand 9 e thus folded back of the carcass ply 9 in the circumferentialdirection respectively. Thereby, the first green tire 101 thus formed iscompleted.

Subsequently, the first green tire 101, shaped like a cylinder, whichhas been formed in the manner as described above, is removed from theforming drum 5 of the first step molding machine 100. A vulcanizerbladder unit 12 is attached to the inside of the first green tire 101thus removed, as shown in FIGS. 4 and 5. The valcanizer bladder unit 12is the same as a vulcanizer bladder unit to be used for inflating acompleted green tire in a curing process which will be described later.The vulcanizer bladder unit 12 is designed to be installed detachably tothe curing machine. The vulcanizer bladder unit 12 is configured of acylinder body 13 of an expandable and contractible structure, which isconstituted of a pair of cylinders 13 a and 13 b movable relatively inthe axis direction and a cylinder-shaped bladder 14 which covers theoutside of the cylinder body 13.

The first green tire 101 for a construction vehicle is extremely heavy.For this reason, the first green tire 101 may be hoisted by a crane witha hook 17 as shown in FIG. 4, or may be carried with a forklift, in aprocess of mounting the first green tire onto the vulcanizer bladderunit 12. In addition, it is preferable that a surface of the bladder 14of the vulcanizer bladder unit 12 may be coated with a mold lubricant 16a by a spray nozzle 16 or the like before the first green tire 101 ismounted onto the vulcanizer bladder unit 12. Furthermore, after themounting of the first green tire 101 onto the vulcanizer bladder unit 12is completed, bead rings 15 and 15 are attached respectively to the twoend portions of the vulcanizer bladder unit 12 as shown in FIG. 5, thusmaking sure that the first green tire 101 does not slip out of thevulcanizer bladder unit 12 easily.

As shown in FIG. 6, subsequently, compressed air is supplied to thevulcanizer bladder unit 12 while the cylinder body 13 of the vulcanizerbladder unit 12 is contracted in the axis direction. Thus, a distancebetween the bead portions respectively on the two ends of the firstgreen tire 101 is set at a predetermined rim width. Subsequently, thebladder 14 is further distended to inflate the outside diameter of thefirst green tire 101 to a diameter in which belts are adhered.Thereafter, the outside diameter of the first green tire 101 is lockedin an inflated condition.

The first green tire 101 which has been set at the predetermined outsidediameter and the predetermined rim width is caused to change itsposition from vertical to horizontal in terms of its axis direction byuse of a turning machine which is not illustrated, while the vulcanizerbladder unit 12 is still being installed to the first green tire 101. Onthe other hand, the forming drum 5 is removed from the drive shaft 3 ofthe first step molding machine 100. Subsequently, the first green tire101, which has been held horizontally as described above, is hoisted bya crane 18 as shown in FIG. 7, or is carried by a forklift, while thevulcanizer bladder unit 12 is still being installed to the first greentire 101. Thereby, the first green tire 101 is mounted onto the driveshaft 3 of the first step mold machine 100 once again.

Then, the first green tire 101 is put into a condition where the drivenshaft 4 of the tailstock 2 is fitted into the first green tire 101mounted on the drive shaft 3 of the headstock 1. In addition, compressedair is supplied from an air supplying unit 19 to the bladder 14 of thevulcanizer bladder unit 12, thereby keeping the first green tire 101 inthe inflated condition. Several plies of belt 20 made of steel cord arewound around the outer periphery of this first green tire 101.Thereafter, tread rubber 21 is wound around the outer periphery of thebelt 20, as shown in FIG. 9. In this manner, the first green tire isformed into a second green tire, namely a completed green tire 102.

The completed green tire 102, which has been obtained in the manner asdescribed above, is removed from the first step molding machine 100while the vulcanizer bladder unit 12 is still being installed to thecompleted green tire 102. Then, the completed green tire 102 isassembled in a vulcanizing mold 22, as shown in FIG. 10. Subsequently,the completed green tire 102 which has been set in the vulcanizing mold22 is heated while being kept in the inflated condition by thevulcanizer bladder unit 12, thus vulcanizing and hardening the completedgreen tire 102. In this manner, the vulcanizing of the radial tire for aconstruction vehicle is completed.

According to the present invention, the second step molding process isperformed as described above. Its main points are as follows. Thevulcanizer bladder unit which has been removed from the curing machineis installed to the first green tire. The first green tire is put intoan inflated condition by this vulcanizer bladder unit, and is installedinto the first step molding machine once again. Thereafter, belts andtread rubber are adhered to the outer periphery of the first green tire.This no longer requires the specialized second step molding machine,which has been essential for the conventional production method. Thepresent invention not only entails no facilities costs for thespecialized second step molding machine, but also requires no space inwhich the second step molding machine would otherwise be installed.Consequently, this enables costs for producing a radial tire for aconstruction vehicle to be reduced to a large extent.

1. A method of producing a radial tire for a construction vehicle, inwhich a first green tire is removed from a first step molding machineafter the first green tire is formed by the first step molding machine;a vulcanizer bladder unit is installed to the first green tire thusremoved, and the first green tire is inflated by the vulcanizer bladderunit; subsequently the first green tire is once again placed in thefirst step molding machine while the vulcanizer bladder unit is stillbeing installed to the first green tire; belts and tread rubber areadhered to the outer periphery of the first green tire on the first stepmolding machine to form the first green tire into a completed greentire; and the completed green tire is assembled into a vulcanizing moldwhile the vulcanizer bladder unit is still being installed on thecompleted green tire to be vulcanized.
 2. The method of producing aradial tire for a construction vehicle according to claim 1, wherein theprocess of forming the first green tire in the first step moldingmachine comprises: mounting a carcass ply cylindrically onto the outsideof a forming drum provided on the first step molding machine;transferring bead core assemblies respectively to two end portions ofthe carcass ply in the axis direction, and folding back the two endportions of the carcass ply to wrap the bead core assembliesrespectively; and winding side rubber around an outer periphery of eachof the two end portions of the carcass ply thus folded back.
 3. Themethod of producing a radial tire for a construction vehicle accordingto claim 2, wherein the process of placing the first green tire to thefirst step molding machine once again comprises: removing the formingdrum from the first step molding machine, and thereafter placing thefirst green tire to the first step molding machine instead of theforming drum.
 4. The method of producing a radial tire for aconstruction vehicle according to any one of claims 1 to 3, wherein asurface of a bladder of the vulcanizer bladder unit is coated with amold lubricant in advance when the vulcanizer bladder unit is installedinto the first green tire which has been removed from the first stepmolding machine.